A technique for detecting objects (for example, other vehicles) approaching the own vehicle by performing image processing on images captured by a camera provided for the own vehicle is known.
As one of the image processing techniques used for the above-indicated technique, a technique is known for identifying an image area of a moving object appearing in the captured images based on an optical flow of the feature point extracted from the chronologically captured images that form the moving images captured by the camera. Note that an optical flow is motion vector information indicating the visible motion of an object on an image, which may be obtained, for example, by searching the corresponding point of the same object (for example, feature point) between two chronological images.
Moreover, a technique is known for detecting an approaching moving object based on an angle difference between a specified approaching direction and a motion vector obtained from a connected block formed by connecting pixels where the angle difference of motion vectors is equal to or less than a specified threshold among pixels that form a captured image.
Further, a technique is known for improving the detection accuracy of moving objects at a long distance with smaller capacity of memory and less computational complexity when moving objects are detected from moving images, where the detection accuracy of moving objects at a short distance is also maintained. In this technique, an attempt is made to detect the motion of an object between chronologically continuous two image frames by using, for example, an optical flow. When such motion is successfully detected, the detected motion is tracked. When the detection of such motion has failed, the motion is evaluated again by using an image frame of the next time or later.
Patent Document 1: Japanese Laid-open Patent Publication No. 64-048181
Patent Document 2: Japanese Laid-open Patent Publication No. 2007-172540
Patent Document 3: International Publication Pamphlet No. 2009/078056